Component Identification

In the 60's their were some germanium transistors still existing in electronic organs, they usually look like a 5 mm LED but about 3 times longer and coated in black you could scrape the black of and use them as photocells, OC71 was the type, think their were aso some that had a metal case and used in early Japanese organs (Hammond Caddette) the only orange transistors I remember seeing were Hitachi and they where silicon NPN, I used  BC182L's to replace them, BC107's or BC109's also work and they have a metal case.

If the organ has been stored in a damp place for a long time the transistors could be a problem, resistor and capacitor problems are pretty rare in transistor circuits. If the resistors don't have a glossy coat they would be more susceptible to damp.

If you have a transistor tester available, some meters might have one built in. their shouldn't be any leakage in good silicon transistors but you get leakage in germanium transistors you need to have a few to test to find ones with the lowest leakage.

I'm assuming you have an oscilator circuit which will probably be one or two transistors and each divider circuit (Octave lower) is usually a pair of transistors, you should be able to put a meter on the collector and should have about half the supply voltage if the divider is working, and zero or supply voltage if not working.. It's easier if you have an Oscilloscope to check the circuits and that the oscillator is running, you can also check the voltages of a working generator boards to compare with the faulty one, same if you have access to a oscilloscope.